How do the rationales of therapeutic approaches for treating bipolar and unipolar disorders compare and contrast?

Unipolar disorder, also called unipolar depression or major depressive disorder, is a single mood disorder in which individuals feel abnormally depressed for a period of at least two weeks. In contrast, those who suffer bipolar disorder will feel both highs and lows; they'll shift from feeling depressed to feeling euphoric, energetic, or manic. Both disorders are treated with biomedical therapy, meaning drug therapy, and types of psychotherapy.Since bipolar disorder is both a mood and a behavioral problem, medications are used to help stabilize a patient's mood while psychotherapy can be used to help a patient control his/her behavior and reduce symptoms. Drugs need to be used to control both manic and depressive moods. Lithium and some antipsychotic drugs can be used to treat both manic and bipolar depressive moods, but antidepressants may need to be used as well. The three psychotherapies that are effective for treating bipolar disorder are cognitive-behavioral therapy (CBT), family-focused therapy, and interpersonal rhythm therapy. CBT is used to help a patient change unhealthy thoughts, beliefs, and behavior patterns. Family-focused therapy (FFT) is used to treat the patient's entire family, not just the patient. Improving relationships with family members helps bipolar patients get well and stay well; therefore, FFT is used to help family members better understand the nature of the disorder, understand behaviors that are negatively affecting the patient, and develop problem-solving strategies. Interpersonal and social rhythm therapy is used to help a patient stabilize his or her mood by stabilizing the daily routine and by fixing relationship problems (National Institute of Mental Health, "Intensive Psychotherapy More Effective"; "Psychotherapies").In contrast to bipolar disorder, antidepressants are primarily used in biomedical therapy for unipolar disorder. While cognitive-behavioral therapy can also be used to treat unipolar disorder, other therapies include psychotherapy, interpersonal therapy, and problem-solving therapy. Plus, since depression is caused by a chemical imbalance in the brain, brain stimulation therapies are also used when a patient is not responsive to other therapies. Brain stimulation therapies include electroconvulsive therapy, transcranial magnetic stimulation, and vagus nerve stimulation (National Institute of Mental Health, "Depression").
https://www.nimh.nih.gov/health/topics/depression/index.shtml